The present invention relates to absorption refrigeration systems and more particularly relates to heat exchangers for absorption refrigeration systems.
In an absorption refrigeration system, relatively cool, weak absorbent solution is usually pumped from an absorber to a generator where heat is provided to boil off refrigerant from the weak absorbent solution to form relatively strong absorbent solution. The relatively hot, strong absorbent solution formed in the generator is returned to the absorber where it is cooled and brought into contact with refrigerant vapor to form the relatively weak absorbent solution which is pumped back to the generator to begin the cycle again.
Conventionally, to improve the efficiency of an absorption refrigeration system, a solution heat exchanger is provided for transferring heat between the relatively hot, strong absorbent solution flowing from the generator to the absorber and the relatively cool, weak absorbent solution pumped from the absorber to the generator. The solution heat exchanger serves to preheat the solution which is to be heated in the generator and serves to precool the solution which is to be cooled in the absorber.
Normally, the generator is located above the absorber and is connected through conduits to the absorber so that the relatively hot, strong absorbent solution flows solely by the force of gravity from the generator through the conduits to the absorber. Typically, in this arrangement, the solution heat exchanger is located below the absorber, which is below the generator, so that during normal operation of the absorption refrigeration system the solution heat exchanger remains full of strong absorbent solution. This leaves a substantial length of conduit, namely, the strong solution line for conducting strong absorbent solution from the generator to the solution heat exchanger, exposed to ambient conditions. If the ambient conditions are expected to be unfavorable, this strong solution line may be insulated to protect the strong absorbent solution flowing through this line from undesirable effects which may occur, such as solidification of strong absorbent solution in this line, due to these unfavorable ambient conditions. However, under certain circumstances, solidification may occur in the strong solution line even if this line is insulated.
In addition, occasionally, difficulty from sources other than ambient conditions is experienced in an absorption refrigeration system of the type described above, due to cooling of the strong absorbent solution in the solution heat exchanger, and/or in the strong solution line for conducting strong absorbent solution from the generator to the solution heat exchanger, below the solidification point of the solution. This may occur, for example, if too much heat is supplied to the generator or if cooling water supplied to the absorber is unexpectedly cold.
When solidification of strong absorbent solution occurs in the solution heat exchanger and/or in the strong solution line for conducting strong absorbent solution from the generator to the solution heat exchanger, strong solution is prevented from flowing from the generator to the absorber. This may result in weak absorbent solution being over cooled in the absorber which, in turn, results in further solidification of strong solution in the solution heat exchanger as over cooled, weak solution is passed through it to the generator. Eventually, the level of solution in the absorber may be lowered to a level such that the solution pump, which forwards weak solution to the generator from the absorber, may run dry thereby damaging the pump. In addition, the strong solution in the generator may rise to a level at which the solution enters the condenser and flows into the evaporator thereby impairing operation of the absorption refrigeration system for a period of time even after the solution heat exchanger is desolidified.
To prevent solidification of strong solution in the solution heat exchanger and/or in the strong solution line for conducting strong absorbent solution from the generator to the solution heat exchanger, from rendering the absorption refrigeration system totally inoperative, a bypass system may be provided for passing excess solution from the generator around the strong solution line and the solution heat exchanger to the absorber. This permits the refrigeration system to operate, at least at partial capacity and efficiency, when the solution heat exchanger and/or the strong solution line are blocked. Also, use of such a bypass system prevents excess solution in the generator from entering the condenser and prevents running the solution pump dry.
At the same time, the bypass system inhibits further solidification in the solution heat exchanger and tends to aid in desolidification because the weak absorbent solution from the absorber, which passes through the unblocked side of the solution heat exchanger, is heated by the generator and then is returned directly to the absorber by the bypass system. This warms the weak absorbent solution in the absorber which, in turn, warms the blockage in the solution heat exchanger when the now warm weak absorbent solution flows back through the solution heat exchanger to the generator.
However, a bypass system as described above, does not aid in desolidification of strong absorbent solution in the strong solution line for conducting strong absorbent solution from the generator to the solution heat exchanger. Thus, such a bypass system may not effectively remedy a blockage due to solidification of strong absorbent solution in this strong solution line. In addition, exposure of this strong line, even if insulated, to ambient conditions is not particularly suitable from the standpoint of maximizing operating efficiency of the absorption refrigeration system.